Combustion-engine exhaust systems



July 2, 1963 R. w. RUMBLE COMBUSTION-ENGINE EXHAUST SYSTEMS 2 Sheets-Sheet 1 Filed Sept. 19, 1960 Awawme July 2, 1963 R. w. RUMBLE COMBUSTION-ENGINE EXHAUST SYSTEMS 2 Sheets-Sheet 2 Filed Sept. 19, 1960 pawn 2 for l. 04454 5' Arrx United States This invention relates to noise abatement systems for combustion engines.

The silencing of engines and especially engine exhausts has occupied the attention of designers from the infancy ofthe combustion engine. As far as concerns road vehicles, the problems have been satisfactorily solved, but with the birth of the jet engine, with exhaust gases moving at very high speeds, silencing is very much to the fore again. The problem appears to be at its most acute when the exhaust stream is supersonic because it is probable that a large proportion of the noise produced is due to the stream decelerating through the sound barrier.

The object of this invention is to propose a method of reducing the noise made by combustion engines and especially by the streams of exhausting gases. I

Sound can only be freely propagated in a gaseous '1'I16d1- um, and the basisupon which the invention proceeds is to form and maintain, around the engine and in particular in the zone of the emergent stream, a condition of reduced pressure which attenuates the sound produced by the stream.

The zone of reduced pressure may be produced by the stream itself, for instance by shaping the conduit through which the stream emerges to induce into the stream flow of air from the annular zone surrounding it. Preferably, however, the'zone. is created by' mechanical means such as a fan driven by the prime mover or by the emergent stream, or both. V

It is also a feature of the present invention that the exhaust stream be broken up into separate parallel streams in a closed pattern with zones of reduced pressure occluded in the streams. Of course the whole stream is still provided with a zone of reduced pressure around its periphery.

Various embodiments of the invention are shown in the accompanying drawings in which:

FIGURE 1 is a longitudinal section through the tail end of a jet engine;

FIGURE 2 is a longitudinal section of a second arrangement;

FIGURE 3 is a cross-section on the line 3--3 of FIG- URE 2;

FIGURE 4 is a longitudinal section through a jet engine;

FIGURE 5 is a side view of one form of nozzle and difluser pipe;

FIGURE 6 is a section on the line 66 of FIGURE 5; and

FIGURE 7 is a side view in section of another embodiment.

In FIGURE 1 there is seen the nozzle 10 of a jetpropulsion engine with the jet stream 12 emerging from the annular duct 14 defined between the nozzle and the hub fairing 16. a

In the immediate vicinity of the nozzle 10, the jet stream, as it leaves the nozzle, is indicated'by chain-dotted lines. In that vicinity the stream behaves virtually like a solid body, that is to say there is no significant diffusion or dissociation at its periphery into the ambient atmosphere. I

In the zone at and immediately behind the nozzle 10, the nozzle and the emergent stream are surrounded by a jacket 18 that defines between itself and the stream a space 20 that is annular or of other cross-section depending upon the shape ofthe nozzle. The jacket has an inward flange 22 that terminates just outside the periphery of the stream 12, so that the space 20 is substantially enclosed.

The jacket is connected to a source of suction by pipes 24.

In use, the space 20 is maintained at a pressure reduced below atmospheric pressure by continuously applying suction to it.. The sound of the emergent stream is attenuated as it traverses the space 20. The noise of the engine is thereby sensibly diminished.

A means of applying suction to the space 20 is shown in FIGURE 4. In this figure a fan 26 is located at the nozzle 28 to be impinged on by the gas stream and rotated. The fan blades 30 are extended beyond the.

nozzle into the space 32 (which, in this case, surrounds the length of the engine), but the blades in the space are of reversed pitch so that they apply suction to the space Y 32 that surrounds the emergent stream.

Alternatively the fan 26 may be driven by the turbine through a shaft33.

At the forward end of the engine the space 32 communicates with the intake 34 to the turbine 36. Air in going to the turbine tends to induce the flow of gas along the space 32 and into the air-stream, so that the entire space 32 is at reduced pressure. Noise evolved by the engine as well as the jet stream is thereby attenuated.

To aid evacuation of the, space 20, one stage 38 of the turbine can be extended into the space 32, as shown at 40, where the pitch of the blade tips is reversed.

In FIGURES 2 and 3, an arrangement as shown in FIG- URE 1, or it may be in FIGURE .4, is used, butwithin the nozzle 42 there is arranged a pattern of vanes-'44 spaced apart to splitthe jet stream into a number of separate channels. ,Between the channels the pressure is reduced. Each channel is thus surrounded by a zone of reduced pressure, and the whole stream is surroundedby a zone of reduced pressure within the space 46.

In FIGURESS and 6 there is seen a baffle structuredefining a pattern of vanes 48' of another kind. Here the area of the nozzle 50* contains an arrangement consisting in a series of pyramidal pockets 52 open 'at their mouths 54 which are directed rearwardly. These pockets occur right round the periphery of the nozzle and also within the 1 nozzle itself. The various pockets 52 define between them a series of spaces 56 through which the jet stream SSemerges.

Beyond the nozzle is a tapered diffuser .tube'60. nozzle and tube may be surrounded by a jacket, as shown in FIGURES 1 to 4, or not.

The nozzle is, of course, dimensioned for the aggregate area of the openspaces 56 to be adequate to pass the jet stream.

The effect of the pockets 53 is that the stream flowing through the spaces 56 (which act as venturis) into the difiuser tube 58 tends to induce flow of air from the pockets 52 into the stream. As these pockets are closed, they are maintained at a reduced pressure which acts to attenuate the noise produced by the jet stream.

In FIGURE 7, it is the jet stream 62 itself that acts to reduce the pressure within the jacket 64. The stream passing through the venturi constituted by the convergent nozzle 65 and the divergentdifiuser tube 66 induces flow The throat of the nozzle 65 may contain a pattern of vanes 70 comprising pyramidal pockets 72 and rearwardly directed aerofoils 74 within the mouths of the pockets. The stream 62 tends to induce flow of air from the pockets and aerofoils, which are maintained under reduced pressure.

In the several embodiments, some reverse flow of the exhaust gases may take place into the enclosed space around the exhaust stream, but the momentum of the stream prevents any reverse flow of significant proportion, and what reverse flow there is does not materially aifect the condition of reduced pressure within the space.

In all figures the nozzle may be circular in section and the jacket likewise; but preferably the jacket and desirably also the nozzle are polygonal, so that sound waves tend to be reflected from the wall of the jacket, or both of them, back into the stream.

I claim:

1. A jet propulsion engine including a conduit for the jet stream and comprisinga convergent nozzle having an inlet mouth disposed at the discharge end of said conduit, a jacket coaxially disposed at and surrounding said nozzle and having a portion extending downstream of said nozzle, said portion having inwardly directed flanges which define an aperture having substantially the same diameter as said convergent nozzle exit mouth, and means being provided in said jacket to reduce the pressure in the space forbed between said convergent nozzle and said jacket to reduce the noise level.

2. An engine according to claim 1 in which said jacket surrounds the conduit along its length defining therewith an annular space of reduced pressure therealong.

3. An engine according to claim 2 in which said means consists of a rotor having turbine blades of a predeterminedpitch mounted in the exit mouth of said convergent nozzle-and being rotated by the fluid flow, said blades having extensions forming fan blades having a different pitchthan said predetermined pitch and being disposed in thespace formed between said convergent nozzle and said jacket, whereby the fan moves gases forwardly with respect to the nozzle.

4. An engine according to claim 1 in which said means consists of a divergent diffuser tube connected to the mouth' of said convergent nozzle, and said jacket contains pipe means connected to a source of suction.

5. An engine according to claim 1 in which said means consists of a divergent diffuser tube disposed within said jacket, one end of said divergent diffuser tube surrounding said convergent nozzle in overlapping relationship but providing an opening therebetween, the other end of said divergent diffuser tube being of greater diameter than said one end thereof and providing another opening between the'other end of said divergent diffuser tube and said jacket, vanes being disposed in the exit mouth of said 7. A jet propulsion engine comprising a convergent nozzle disposed-atthe discharge end of said engine for discharging the exhaust thereof, a divergent difiuser tube having one end the same diameter as said convergent nozzle exit and being mounted thereon,'said divergent diffuser tube extending in progressively-increasing diameter to the other'en'd thereof, ajacket having one end surrounding said convergent nozzle and the one end of said divergent diffuser tube and containing a portion extending downstream and beyond the other end of said divergent difiuser tube and means to reduce the pressure within the space between said divergent difiuser tube and said jacket, said-portion having inwardly directed flanges to define an aperture having substantially-the same diameter as said convergent nozzle exit, and a baffle structure disposed in said convergent nozzle to divide the exhaust 4 into a number of separate channels to reduce the noise level of the engine.

8. A jet propulsion engine according to claim 7 in which said jacket is connected to a source of suction.

9. A jet propulsion engine according to claim 7 in which the one end of said divergent diffuser tube has an overlapping portion which overlaps said convergent nozzle in spaced relationship to define an opening therebetween, the other end of said divergent diffuser tube terminating in spaced relationship with respect to said jacket to define a further opening therebetween.

10. A jet propulsion engine according to claim 7 in which said bafiie'structure consists of a number of closed pyramidal pockets provided with rearwardly directed and spaced apart mouths.

1-1. A jet propulsion engine according to claim 10* in which rearwardly directed aerofoils' are disposed within the rearwardly directed and spaced apart months.

12. A jet propulsion engine according to claim 7 in which said baffle structure consists of a number of rearwardly directed aerofoil vanes.

13. A jet propulsion engine comprising a turbine mounted therein, an intake disposed in the rfront part of said engine and communicating with said turbine to lead a fluid thereto, a convergent nozzle disposed in the back part of said engine and communicating with said turbine for discharging the exhaust fluid therefrom, a jacket surrounding substantially the entire length of said engine and spaced therefrom to define a space of reduced pres sure, said jacket having a portion extending beyond said convergent nozzle, said portion of said jacket terminating into inwardly directed flanges defining an aperture having substantially the same diameter as said convergent nozzle,

and a fan disposed at the discharge end of said convergent nozzle having turbine blades of a predetermined pitch located within the path of the exhaust discharging from said convergent nozzle, said turbine blades containing extensions having another pitch different from said' pre determined pitch disposed in the space of reduced pressure between said jacket and said'convergent nozzle, to reduce the noise level of the engine.

.14. A jet propulsion engine comprising a turbine mounted therein, an intake disposed in the front part of said engine and communicating with said turbine to lead a fluid thereto, a convergent nozzle disposed in the'back part of said engine and communicating with said turbine lfOl discharging the exhaust fluid therefrom, a jacket surrounding substantially the entire length of said engine and spaced therefrom to define a space of reduced pres sure said jacket having a portion extending beyond said convergent nozzle, said portion of said jacket terminating into inwardly directed flanges defining an aperture having substantially the same diameter as said convergent nozzle, and a fan disposed at the discharge end of said convergent nozzle having turbine blades of a predetermined pitch located within the path of the exhaust discharging from said convergent nozzle, said turbine bladescontaining extensions having another pitch different from said predetermined pitch disposed in the space of reduced pressure between said jacket and said convergent nozzle to reduce the noise level of the engine; the turbine having a further fan mounted thereon, said further ran contains blades having a predetermined pitchdisposed within said intake and each blade of said further lfan contains extensions disposed within the space of reduced pressure and having a difierent pitch from the predetermined pitch of the blades of said further fan.

Kadenacy Aug. 8, 1939 Servanty Nov. 20, 195.1

(Other references on following page) V UNITED STATES PATENTS FOREIGN PATENTS 2,620,624 Wislicenus Dec. 9, 1952 1,114,647 France Dec. 19, 1955 2,637,166 Carswell May 5, 1953 1,199,576 France June 22, 1959 2,674,087 Russell Apr, 6, 1954 1,208,542 France Sept. 14, 1959 2,300,7 5 Fren h July 0, 1957 5 654,344 Gr a Br1 n n -1 95 1 2,882,679 Kancher et a1. Apr. 21, 1959 783,003 Great Brltam Sept 18, 1957 2,892,582 ORourke June 30, 1959 OTHER REFERENCES 2915136 Rlggleb Dec-1,1959 Harris: Handbook of Noise Control, chapter 33; 2,920,445 Balley Jan. 12, 1960 10 pages 35 and 36, copyright 1957 by McGraw-Hill Book 2,974,744 Wade M313 1961 Company, Inc, New York,

3,009,318 Skoff Nov. 21, 196 1 

1. A JET PROPULSION ENGINE INCLUDING A CONDUIT FOR THE JET STREAM AND COMPRISING A CONVERGENT NOZZLE HAVING AN INLET MOUTH DISPOSED AT THE DISCHARGE END OF SAID CONDUIT, A JACKET COAXIALLY DISPOSED AT AND SURROUNDING SAID NOZZLE AND HAVING A PORTION EXTENDING DOWNSTREAM OF SAID NOZZLE, SAID PORTION HAVING INWARDLY DIRECTED FLANGES WHICH DEFINE AN APERTURE HAVING SUBSTANTIALLY THE SAME DIAMETER AS SAID CONVERGENT NOZZLE EXIT MOUTH, AND MEANS BEING PROVIDED IN SAID JACKET TO REDUCE THE PRESSURE IN THE SPACE FORMED BETWEEN SAID CONVERGENT NOZZLE AND SAID JACKET TO REDUCE THE NOISE LEVEL. 